The SureFire X400 combines a brilliant white light with a bright green laser aiming device in one WeaponLight. A high-efficiency LED generates 500 lumens of brilliant white light focused by a Total Internal Reflection (TIR) lens to produce a tight beam with good reach and significant surround light for peripheral vision and situational awareness. The LED has no filament to burn out or break and generates tactical-level light bright enough to overwhelm an aggressor's night-adapted vision for 1.5 hours per set of batteries. The 5-milliwatt, 635 nanometer laser sight, located below the primary light, is nearly twice as bright and much more visible than the nearest competitor. The laser's adjustment mechanism uses Nylok screws that won't back out from the effects of recoil, which means it rarely needs to be re-zeroed.

The white light/laser combination makes the X400 effective in close- to medium-range engagements, ideal for law enforcement, military, and self-defense use. The high-strength aerospace aluminum body is Mil-Spec hard anodized for superior toughness and corrosion resistance, and is O-ring and gasket sealed to make it weatherproof. The X400 comes with two adapter wedges permitting rapid attachment to and removal from either Universal or Picatinny rails. An ambidextrous push/toggle switch provides one-finger operation for either momentary or constant-on operation, and a mode switch allows you to select white light only, white light plus laser, laser only, or system disable. Optional pistol grip switches permit operation with the top grip finger, leaving the index finger free to operate the handgun trigger. Other switches are available for operating the X400 when attached to a long gun.